Production techniques for colouring agents and pigments by diazo-coupling reaction are well known, and a large number of pigments has been obtained in this manner.
The pigment listed in the Color Index as Pigment Yellow 74 is obtained by diazotizing of 2-methoxy-4-nitro-aniline (PNOA) and coupling with acetylaceto-2-anisidide (AAOA). This is a very greenish yellow pigment, which is widely used in the paints and printing inks industry.
PY 74 is found commercially in two forms, one transparent and of high colouring power, the other opaque and of lower colouring power, used mainly in paints, where covering properties are very sought after.
According to document EP 0079303 A, the transparent form is obtained by heating after coupling at 70.degree. C. and immediate filtration. The opaque form results from the same coupling reaction and the heating of the reaction mixture to boiling point for one hour before filtration. It is specified that the difference in the colouring power results from the difference in the crystalline dimensions rather than from different crystalline forms.
The purpose of this document is to improve the opaque form of PY 74 in order to overcome the problem linked to the loss of colouring power on storage by tinting (chemical modification) the PY 74 with 1 to 20%, and preferably 2.5 to 7%, of another mono-azo yellow pigment based on acetylaceto-2-anisidide.
The document mentions that the mixture can be obtained:
by mixing the two constituents while dry, PA1 by mixing the filter cakes of the two pigments, followed by drying, PA1 by diazotizing of a mixture of the respective aminated precursors (anilines), followed by coupling, boiling, filtration and standard drying, PA1 by separate diazotizing of the two precursors, followed by a mixture of the two diazotized compound solutions, coupling, boiling, filtration and drying, PA1 by diazotizing and coupling of the precursors in separate operations and mixing the aqueous sludges, followed by standard boiling, filtration and drying operations or also PA1 by diazotizing and coupling of one of the precursors followed by separate diazotizing of the second precursor and coupling in the presence of the first pigment followed by standard boiling, filtration and drying operations. PA1 In printing inks, the product which is most transparent and has the greatest colouring power is generally preferred. PA1 power and transparency on the one hand, PA1 good flow properties on the other hand.
The tinting compound is obtained from one or more amines of formula (R.sub.1).sub.m --(R.sub.2).sub.n --C.sub.6 H.sub.4 --NH.sub.2 (m+n.ltoreq.3), where R.sub.1, R.sub.2 represent alkyl, alkoxy, halogen (in particular chlorine) or nitro groups.
The 4-nitro-2-amino-anisole, 4-methyl-2-nitro-aniline, 2-methyl-5-nitro-aniline and 3-nitro-4-amino-anisole amines are described as being particularly useful as precursors.
In document FR 2394584 A, a mixture constituted by 75 to 85% by weight of PY 74 and 25 to 15% by weight of a pigment identified in the color index as pigment yellow 65 (PY 65) is claimed.
The mixture can be obtained by a process characterized in that 0.75 to 0.85 molar equivalent of 5-nitro-2-amino-anisole and 0.25 to 0.15 molar equivalent of 3-nitro-4-amino-anisole are diazotized, and the diazo compounds are coupled with acetylaceto-amino-2-anisole (referred to as mixed coupling). It is indicated however that the mixture can be achieved by an intimate mixture of the constituents in the ratio indicated.
It is indicated that these mixtures constitute a yellow verging more on the red than PY 74. They both have a tinctorial power and a tint very similar to those of pigment yellow 12 (PY 12) used on a large scale in the printing industry, but they are distinguished by a much improved fastness to light as well as a higher transparency, a stronger gloss and good fluidity in binding systems. These mixtures are superior to equivalent mixtures obtained using 3-nitro-4-amino-anisole and 4-chloro-2-nitro-aniline as diazotizing components.
Various uses for dying, printing paper and synthetic materials, in the preparation of printing inks and paints are mentioned.
Other mixtures of pigments based on PY 74 have been described, in particular in the document GB 1 348 509 A (mixtures derived from a diazo compound and 0.5 to 20% of one or two polar couplers) and in the document FR 2226440 A (derivatives of 4-nitro-aniline).
In the document FR 2275533, PY 74 is treated with salts of alkylamines or aralkylamines and colophanes, in order to improve the stability of transparency when hot, dispersibility and rheology. The PY 74 can optionally be tinted using components intended to obtain a redder shade.
Finally, in document EP 0012944 A, the objective is to increase the stability on recrystallization by using mixtures of pigments derived from several amines or couplers, 1 to 20% of which contain acid groups which are then subjected to treatment with quaternary cationic compounds.
Other documents report improvements on mono-azo pigments obtained by tinting (coprecipitation on synthesis).
The document Database WPI, Section Ch, Week 7604, Derwent Publications Ltd., London, GB; Class E24, AN 76-06814X, XP002057434 & SU 405 382 A claims a pigment of high quality obtained by diazotizing of a mixture based on 4-chloro-2-nitroaniline and coupling with acetylaceto-m-xylidide.
The document U.S. Pat. No. 3,446,640 A mentions transparent and stable pigments obtained by diazotizing of 4-chloro-2-nitroaniline and coupling with a mixture of acetylacetanilide and acetylaceto-m-xylidide.
Finally, the document "An investigation in the synergism of monoazoacetoacetanilide pigments", Liu Dongzhi et al., Dyes and Pigments, 18, no. 1, Jan. 1, 1992, pp. 69-80, indicates that when there is synergy, pigments with improved colouring power and transparency are obtained, combined with primary crystals of smaller size.
Document EP 0079303 A mentioned above indicates the modifications to the process which allow the transparent form or the opaque form to be obtained.
In fact, it is possible to obtain all the variants of the product, from the most transparent to the most opaque, by modifying the process parameters, the main point being the intensity of heating (temperature and duration) after coupling: when the heating is increased, transparency and colouring power decrease, as does the gloss of the ink.
However, other characteristics are correlated to the same properties, which limit the possibilities. It is generally accepted that the flow properties (rheology) of the pigmented ink quite particularly become worse and worse as the colouring power and transparency increase. This is particularly unsatisfactory for the production of concentrated inks (with a high pigment content).
The purpose of the present invention is to provide compositions based on PY 74 allowing a practical optimum level to be obtained which is superior to current products, while reconciling properties which are a priori contradictory: